Shuttle foam likely hit wing further out

Blow would cause serious gap on the wing, board says

Columbia accident investigators said Tuesday that a chunk of flying foam insulation hit the orbiter's left wing farther out than previously believed.

If the assessment is correct, the blow may have deformed, loosened or dislodged a large, slender U-shaped carbon composite component called a T-seal.

That would leave a dangerous gap in the wing's thermal armor, perhaps just 1 1/8-inch wide and several inches long, said Harold Gehman, the retired U.S. Navy admiral who is leading the accident probe.

Experts working for the Columbia Accident Investigation Board are already doing a range of thermal analyses to determine whether a slit, rather than a large hole, would have permitted enough heat to invade the left wing and triggered the shuttle's fatal disintegration Feb. 1 over North Texas.

The latest theory from the 13-member investigative panel is based on several sources of information:

· Continuing enhancements of a once-blurry launch film and video made of Columbia's Jan. 16 liftoff.

· Military radar returns from an object that drifted away from the shuttle during the second day of the mission.

· Examination of wreckage gathered along the shuttle's flight path.

· Data recorded by the flight recorder recovered March 19 near Hemphill.

Each seems to tell a slightly different story. Investigators hope to resolve those differences with a series of foam-impact tests at the Southwest Research Institute in San Antonio beginning late this month.

The ongoing film analysis now appears to place the foam impact point between the seventh and eighth of the 22 U-shaped carbon composite panels that line the left wing's leading edge.

The previous impact site was believed to center on panel six, closer to Columbia's fuselage.

For weeks, experts at the Wright Patterson Air Force Base near Dayton, Ohio, have been trying to identify the mysterious object captured on military radar floating away from Columbia.

Until this week, the lab analysis at Wright Patterson suggested the object was a "carrier panel," a four-inch wide metal fixture that rests underneath the wing between each leading-edge carbon panel and the larger lower wing surface.

But the suspect carrier panels have been recovered, with little sign of burn-through. Also, with more refined testing, investigators now believe a T-seal or perhaps a broken U-shaped carbon panel is a better match. More radar analysis is planned.

Soon after the flight data recorder was recovered, NASA engineers began deciphering the information on a magnetic tape from 721 temperature, pressure and stress sensors embedded in Columbia's fuselage and wing.

Sensors positioned behind carbon panel nine and at the intersection of panels nine and 10 of the left wing noted a sharp rise in temperature after Columbia dipped into the Earth's atmosphere to begin the long gliding descent toward Kennedy Space Center in Florida.

The temperature readings, though in the right place to support damage near the eighth and ninth panels, may not be absolute confirmation. They were the only devices recording temperatures anywhere close to the wing damage, said Hubbard.

On the other hand, debris recovered from this area showed extreme, prolonged heat damage, he said.

Trying to calculate the force of the foam strike on Columbia's left wing has also been tricky. The object was estimated to be 25-by-15-by-5 inches, weighing 2.4 pounds per cubic foot and traveling 650 feet per second. Further, it glanced off at a 10-degree angle.

That yielded an estimated 1,700 pounds of force, said board member Douglas Osheroff, a Nobel laureate.

One thought is that perhaps the impact sheared the 1/4-inch bolts that hold down the pieces of the carbon leading edge or the T-seal.

"That doesn't sound like a lot on a pristine steel bolt," said Chad Landis, a Rice University professor of mechanical engineering and materials science.

The key word was "pristine," he said. Corrosion has been a recurring theme in the board's work.

If a single bolt took all 1,700 pounds of the impact, that would be a force of roughly 34,000 pounds per square inch, Landis said. But a healthy 1/4-inch bolt should have a sheer strength of perhaps 50,000 pounds per square inch.

"A new bolt should be able to handle that. This is an interesting engineering problem and it has a lot of features to it," he said.

The investigative board will call off 10 weeks of intensive search for Columbia wreckage along a swath of East Texas by April 30.

The search for wreckage, conducted largely by between 5,000 and 6,000 personnel daily from the U. S. Forest Service and state forest service personnel from Texas and a number of western states, has so far produced 78,000 pounds of wreckage, or nearly 37 percent of Columbia's mass.

Limited close-quarter searching will continue along a corridor 40 miles west of Interstate 45 at Corsicana and at sites in Nevada, Utah and West Texas, where fragments of the stricken shuttle may have fallen away.